1. Field of the Invention
This invention relates to a storage rack system in which goods are loaded onto pallets which are moved by lift trucks and, more particularly, to a storage rack system of the push-back type.
2. Description of the Prior Art
Two-deep push-back systems have been in use since the late 1950's, whereas, three-deep and four-deep systems are of more recent vintage. Typical of these are the systems issued to D. Allen in U.S. Pat. Nos. 4,955,489; 4,949,852; and 5,184,738.
In U.S. Pat. No. 4,955,489, there is described a storage rack system of the push-back type; whereas, U.S. Pat. No. 4,949,852 covers a three-deep and four-deep system having a double cart assembly wherein a large cart rides on the tracks and a small cart is movably mounted onto a large cart.
U.S. Pat. No. 5,184,738 covers a storage rack system adapted to store pallet loads that are three, four, and five pallets deep.
Basic to all of these is the pioneer storage rack systems covered by U.S. Pat. No. 4,341,313 issued to E. Doring.
Another system of interest is the three pallet assembly covered by A. Konstant in U.S. Pat. No. 4,773,546.
In this system, the carts ride on the lower flange surfaces of parallel I-beams. More particularly, two pairs of I-beams are arranged to provide a pair of inwardly facing flanges for one track, whereas, the outwardly facing flanges provide the other track so that an upper cart may ride on one of the tracks while a lower cart rides on the other. Each I-beam is supported by an interior shelf beam to which it is secured by brackets.
However, the Konstant system is not without its disadvantages. For one, the I-beam flanges are not only narrow and provide little track means but the I-beams extend linearly over a considerable distance due to the fact that commercially available I-beams are used. The disadvantage is that I-beams have a tendency to roll and become distorted and twist to some degree.
If this distortion were not compensated for, the wheels of the carts would come into contact with the web of the I-beam as they move along the tracks, and this would impede their movement and lead eventually to wheel failure. It is for this reason that Konstant secures the I-beams to interior shelf beams shelf beams by the use of brackets.
Still, the sloped surfaces of the I-beam flanges create other problems. For example, the cart wheels are required to roll at an angle, that is, they roll on a sloped surface, not a flat surface. As a result, there is a tendency for the wheels to ride up the flange in the direction of the I-beam web where they engage both the upper and lower flange surfaces and become wedged.